mickeych Posted September 30 Share Posted September 30 We are using a decentralised approach to MVHR in part of our build and we are ordering windows right now. Does anyone know whether building control will still need trickle vents in a room that is served by a single room MVHR? (No response from Building Control after asking the question!) Link to comment Share on other sites More sharing options...
JohnMo Posted September 30 Share Posted September 30 MVHR and dMVHR does not need trickle vents. You have to have dMVHR in every room, for it to be sound ventilation strategy, so stupid expensive and you have to meet the minimum whole house flow rates. Have to you considered cascade MVHR instead? Or proper MVHR with coanda effect terminals, or a combination of the two to limit ducts? 1 Link to comment Share on other sites More sharing options...
Dave Jones Posted September 30 Share Posted September 30 not heard of cascade system, could be a cost effective alternative only having to duct the extract rooms. Link to comment Share on other sites More sharing options...
JohnMo Posted September 30 Share Posted September 30 2 minutes ago, Dave Jones said: not heard of cascade system, could be a cost effective alternative only having to duct the extract rooms. Cascade is a system configuration used by people like Fresh-R also a configuration used by Brink. Just as effective as normal MVHR, infact most MVHR is using cascade to a lesser extent. For example lounge is supplied with air, air then moves though the hall and is extracted in the kitchen, the hall is ventilated via cascade. Link to comment Share on other sites More sharing options...
Nickfromwales Posted September 30 Share Posted September 30 I've heard that single room MVHR is less than brilliant, particularly with regards to actual heat recovery. If true "fresh in / stale out" then trickle vents become redundant / unnecessary. Most BC officers don't have a Scooby-Doo tbh. 1 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 1 Share Posted October 1 (edited) 12 hours ago, JohnMo said: Cascade is a system configuration used by people like Fresh-R also a configuration used by Brink. Just as effective as normal MVHR, infact most MVHR is using cascade to a lesser extent. For example lounge is supplied with air, air then moves though the hall and is extracted in the kitchen, the hall is ventilated via cascade. the big drawback is loss of heat though with this. fresh air is drawn in at outside temp by trickle vents leading to high moisture issues in winter. Edited October 1 by Dave Jones Link to comment Share on other sites More sharing options...
mickeych Posted October 1 Author Share Posted October 1 12 hours ago, JohnMo said: Cascade is a system configuration used by people like Fresh-R also a configuration used by Brink. Just as effective as normal MVHR, infact most MVHR is using cascade to a lesser extent. For example lounge is supplied with air, air then moves though the hall and is extracted in the kitchen, the hall is ventilated via cascade. Ok. I looked at the Fresh R option a few months ago and reckoned that the same principle could be used with connected lower cost dMVHR units such as the Blauberg ones. We are using a single centralised MVHR in the new build part of the build (kitchen, breakfast, utility, boot-room and laundry) as we were able to design it into the fabric, but much more tricky with the old stone barn as we have no capacity for ducting. I spec'd trickle vents for the bedrooms as I am not entirely sure that we will have the capacity or desire to put additional units into these rooms (and holes in 600mm listed stone walls), but we do need something to provide airflow into the open plan living area and snug. My idea was to use a pair of linked in/out dMVHR one in the hall and one in the main open plan area which we set to run so that one 'pushes' air whilst the other 'pulls' air hoping that this then helps deal with the issues of using a single unit. Thoughts on this... Link to comment Share on other sites More sharing options...
Dave Jones Posted October 1 Share Posted October 1 ask bpc to design you a solution, they dont charge for this. Link to comment Share on other sites More sharing options...
JohnMo Posted October 1 Share Posted October 1 2 hours ago, Dave Jones said: the big drawback is loss of heat though with this. fresh air is drawn in at outside temp by trickle vents leading to high moisture issues in winter. No, there are no trickle vents, it is MVHR, just implemented with minimal ducts Link to comment Share on other sites More sharing options...
JohnMo Posted October 1 Share Posted October 1 1 hour ago, mickeych said: but much more tricky with the old stone barn as we have no capacity for ducting. I spec'd trickle vents for the bedrooms as I am not entirely sure that we will have the capacity or desire to put additional units into these rooms (and holes in 600mm listed stone walls), but we do need something to provide airflow into the open plan living area and snug. You have to very careful mixing strategies as even with the bedroom trickle vents the bedroom may not be properly ventilated as you don't get a draw through from any fans elsewhere. Do you have a basic plan you can post up, there maybe some simple solutions. Also how airtight are you planning if not below 3 for the whole house MVHR may not be right solution for either part of the house 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 1 Share Posted October 1 12 minutes ago, JohnMo said: Also how airtight are you planning if not below 3 for the whole house MVHR may not be right solution for either part of the house What he said... Link to comment Share on other sites More sharing options...
mickeych Posted October 1 Author Share Posted October 1 8 hours ago, Nickfromwales said: What he said... We were aiming at around 3 -3.5 but this what the SAP calcs came in at: Air permeability [AP50] = 5.0 m³/h.m² (assumed) Since we had these done we have opted to tank the whole of the original barn up to eves so I presume if this is all lapped into the membrane well, it should give us a greater level of tightness. Link to comment Share on other sites More sharing options...
mickeych Posted October 1 Author Share Posted October 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 3 Share Posted October 3 On 01/10/2024 at 20:01, mickeych said: We were aiming at around 3 -3.5 but this what the SAP calcs came in at: Air permeability [AP50] = 5.0 m³/h.m² (assumed) Since we had these done we have opted to tank the whole of the original barn up to eves so I presume if this is all lapped into the membrane well, it should give us a greater level of tightness. Stopping at the eaves will leave a huge amount of permeability, so I doubt this is anything to hang your hat on, and if 3-3.5 is the target then you'll have fabric infiltration beyond the flow rates of the MVHR which means the heated air will be getting lost faster that the MVHR unit can recover it, so consider your next move based on the worst case scenario so you don't make any unwise investments here. Link to comment Share on other sites More sharing options...
mickeych Posted October 3 Author Share Posted October 3 8 hours ago, Nickfromwales said: Stopping at the eaves will leave a huge amount of permeability, so I doubt this is anything to hang your hat on, and if 3-3.5 is the target then you'll have fabric infiltration beyond the flow rates of the MVHR which means the heated air will be getting lost faster that the MVHR unit can recover it, so consider your next move based on the worst case scenario so you don't make any unwise investments here. I'm guessing that the options are limited to throwing more money at making the building more airtight vs fitting trickle vents and leaving out MVHR. What do you suggest are the options? Link to comment Share on other sites More sharing options...
Mike Posted October 3 Share Posted October 3 1 hour ago, mickeych said: the options are limited to throwing more money at making the building more airtight vs fitting trickle vents and leaving out MVHR Making the building more airtight + adding MVHR is undoubtedly the best option. It doesn't have to involve throwing lots of money at it, but does require a well implemented plan. Post some sketches of the roof junction and you'll probably get some suggestions of how to do that. Though there are probably already be other threads on the topic that will give you ideas too. 1 Link to comment Share on other sites More sharing options...
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